1. Field of the Invention
The present invention relates to a noncontact IC tag with a non-conductive metal film. More particularly, the present Invention relates to a noncontact IC tag that has a lustrous deposited metal film but is non-conductive, and that is excellent in communication performance. Although the noncontact IC tag with a non-conductive metal film according to the present invention can be used as an ordinary noncontact IC tag, it is particularly favorable for applications where metallic IC tags having decorative properties are desirable.
The technical field of the invention is the production and use of noncontact IC tags. The noncontact IC tags of the present invention are useful mainly in the fields of transportation, distribution, sales control, process control, delivery of commodities, and luggage handling. Specifically, they can be used as tags, labels, slips, tickets, and the like.
2. Background Art
Noncontact IC tags have come to be used widely as identification media in the fields of transportation, distribution, and the like, or for such purposes as quality control, stock control, etc. of commodities, because information can be recorded and stored in them and the stored information is exchangeable by communication with external devices without bringing them into contact with the devices.
In order to meet demand for a decorative noncontact IC tag with a beautiful metallic luster, if a metal material such as aluminum foil or a conventional metallized material is used as the substrate of a noncontact IC tag, the IC tag causes communication failure, so that it cannot be used practically.
A possible cause of the above-described communication failure is as follows: eddy current flows in the metal film owing to the AC magnetic field produced by electromagnetic waves which the noncontact IC tag uses for data transmission/reception; this eddy current produces magnetic flux that repels the magnetic flux for data transmission/reception; the magnetic flux for data transmission/reception is thus reduced, which makes data transmission/reception difficult.
Another possible cause of the above-described communication failure is as follows: an antenna or coil made from an electrically conductive material forms a condenser together with the metal film; the stray capacitance produced by the condenser alters the inductance of the antenna or coil, and the resonance frequency characteristic of the condenser.
Noncontact IC tags with deposited metal films have a metallic luster that can never be expressed by printing, and are sophisticated in design, and it is very easy to locate them even if they have been attached to articles. For this reason, it is expected that such noncontact IC tags will be increasingly adopted in various fields. Effective measures should now be taken to prevent noncontact IC tags with deposited metal films from causing troubles, due to the deposited metal films, in communication with reader/writers.
In the meantime, there have been known techniques using deposited metal films of islands-in-sea structure as described in the following Patent Documents 1 to 4. The islands-in-sea structure (also referred to as island structure or islands) is that minute, discrete metal deposits (small islands) constitute a metal film (sea), and the surface of such a metal film deposited has been known to be non-conductive. However, none of these Patent Documents proposes the use of deposited metal films of islands-in-sea structure for noncontact IC tags. Technical literatures describing the formation of films of islands-in-sea structure, etc. include the following non-Patent Documents 1 and 2.
Patent Document 1: Japanese Laid-Open Patent Publication No. 174189/1987.
Patent Document 2: Japanese Laid-Open Patent Publication No. 157858/1988.
Patent Document 3: Japanese Laid-Open Patent Publication No. 249688/1988.
Patent Document 4: Japanese Patent Publication No. 2703370.
Non-Patent Document 1: Chapter 1-Shinku-jochaku-ho (or Vacuum Deposition Processes) (I-93 to I-95) of “Hakumaku-Kogaku Handbook (or Thin Film Engineering Handbook)”, edited by Thin Film Committee No. 131, Nlhon Gakujutsu Shinko-kai, published by Ohm, Tokyo, Japan in 1972.
Non-Patent Document 2: Chapter 1-Shinku-jochaku-ho (or Vacuum Deposition Processes) (pp. 10-16, and 50-51) (by Sadafumi YOSHIDA) of “Hakumaku (or Thin Film)” compiled in Oyobutsurigaku-Sensho 3 published by Baifu-kan, Tokyo, Japan in June 1990.
It is impossible to give a metallic luster to noncontact IC tags by any of the prior art techniques because if a metal is deposited on any constituent layer of a noncontact IC tag, the deposited metal film makes the IC tag poor in communicational performance. We thought that non-conductive deposited metal films of islands-in-sea structure could solve this problem in the prior art. We made earnest studies to prove our idea, and, as a result, achieved the present invention.